Mt. Hood avalanche leaves mark

Nature flung a rock scarf flung down the northeast shoulder of Mt. Hood.

Sometime in the last few weeks, a mile-long rock avalanche happened on Newton Creek glacier. Photographer Darryl Lloyd of Hood River noticed it Aug. 19 and hired a pilot to take him for a closer look. Lloyd said on Aug. 27 that he believes the slide happened in the past few weeks.

He reported it to Richard Iverson, hydrologist with the United States Geological Survey, who said he viewed the slide for the first time Thursday, and plans to check it out on the ground Wednesday, along with other colleagues from the Cascade Volcano Observatory in Vancouver, Wash.

"It is relatively fresh, though we don't know when it occurred," Iverson said. "It was in the last few weeks, based on the appearance of the rock.

"It's pretty clear it originated on the headwall of Newton Glacier, and spilled out over the glacier," he said. "Not much of it made it beyond the glacier."

Lloyd describe the avalanche debris as "yellowish, pulverized" material, with a few house-sized boulders.

The slide was first thought to be close to a year old, but Iverson has revised that estimate, based on his aerial examination, as well as other circumstances.

"My favorite guess is it happend last week during that heavy rain we got. It might explain why no one heard it," as few people were on the mountain because of the bad weather. Or, it could have happened in the dead of night.

Originally, Iverson had thought the slide was the one in November 2000 that caused massive washouts in Newton Creek and White River. But upon further examination, it appears this slide is a new one with an older rock avalanche that underlies it, he said.

"The lower tongue of yellowish-looking debris into Newton Creek valley is older deposit," he said. The new avalanche was "roughly a few hundred thousand cubic meters," in volume, he said. However, very little appears to have entered any local streams.

"It all stayed high, close to where it originated, and didn't have the momentum to go further than it did," Iverson said

He said that "in the grand scale, geologically, this is not terribly important, in that it has not impacted on resources or structures.

"But it is a good example of the kind of event that could occur on a much larger scale. Then it would have real ramifcations," Iverson said.

"With such light snowpack, the glaciers are largely bare ice and it could be that had there been more of a snowpack it might have mobilized and turned into a slurry and made its way downstream," Iverson said.

Ultimately, this new slide won't change the appearance of the mountain, Iverson said.

"You rally have to look at it pretty cloely to see where it came from," he said. "There's brighter rock exposed with peeling away of old rock, but with time it will weather to the color of its old rock."